Homework Help: Chemistry

Posted by Angeline on Monday, April 20, 2009 at 9:05pm.

Posted by Angeline on Monday, April 20, 2009 at 5:35pm.

A few questions...how many grams are in 48.7x10^24? I don't know how to convert atoms to grams. I can do moles to grams or moles to atoms, but not atoms to grams. My other problem is how do you convert moles to moles as in "how many moles of Cu2O are needed to produce 2.3 moles of Oxygen gas?" The answer is two according to my friend, but I want to know how they reached this. Thanks for your help.

Responses

Chemistry - GK, Monday, April 20, 2009 at 7:26pm
Convert the number of atoms to moles by dividing by 6.02x10^23 atoms/mole.
Once you have the number of moles, you multiply by the formula mass ( grams/mole) to get the number of grams.

Chemistry - Angeline, Monday, April 20, 2009 at 9:04pm
Would the answer then be 971.57 grams?

Chemistry - DrBob222, Monday, April 20, 2009 at 9:28pm
You don't show the molar mass or the compound so we don't know how many grams. Do what GK suggested to find the moles, then multiply by the molar mass.
For the Cu2O part of the problem, the secret tip is to write a balanced equation.
2Cu2O ==> 2Cu + O2
The equation TELLS you that 2 mols CuO will produce 1 mol O2.
You can do this by ratio/proportion or you can use the dimensional way of doing it. The dimensional way is to start with what you have (2.3 mols Oxygen is what you want) and convert that to moles Cu2O.
2.3 mols O2 x (2 mols Cu2O/1 mol O2) = ?? Notice how the units cancel. We don't want moles O2 (and they cancel) and we want the answer to be in mols Cu2O and that unit does not cancel.

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